ESD system and time delay in closing valves

hisham

I would like to know from the design point of view. If we have ESD ZV, is it possible or recommended to make the valve closes with time delay. We have 5 valves 3 of them closes with 10 to 20 seconds delay. I suspect that there is time delay set in the PLC logic. Does this sound logical when we have triconex ESD system?

Hisham

I checked with our engineering and they confirmed that their should not be any delay. I did check the power suplly coming to the selnoid and it became energized the moment we press the close push button. We opened then the pilot and did the necessary cleaning ,but we still have the problem.

ESD

It has been confirmed by our engineering that the PLC logic used cannot be other than yes or no or in another way 1 or zero as you know. I need to know though that can modern PLC configured to to have some delay if we wish.

(Any way the problem was solved as lot of dirt was found in the pilot valve as probably the LPG loading rack was out of service for a long time and that cause the dirt to accumulate)

Tom Chubb

Further adding to Francis regarding the vent pipework, if you are able to hear it venting throughout the 20second closing time this would effectively prove that the vent pipework is too small/too long.

Ahmed Attia

The paragraph that mentions the 45 second requirement is in Appendix C - Support Systems. The paragraph begins on page 65, C.2.1.4 Supply and Response. The last sentence on page 65 continues on page 66 with the 45 second requirement.

"The time it takes for any safety device (e.g. PSH, BSL, ESD station, etc.) to effect component or platform shutdown should not exceed4 5 seconds. To achieve this response, consideration should be given to pneumatic line sizes, safety device bleed port size and the use of auxiliary quick bleed devices. Pneumatic lines that supply and bleed should be sized for optimum bleed conditions. Because of volume and flow characteristics a line that is either too large or too small will require excessive time to bleed."

The next sentence applies an obsolete API Recommended Practice 550 to be used as a guide when designing instrument and control systems. Instead the paragraph should reference 551-554, etc.

>Not sure what the last two letters mean but if ESD stands
>for "Emergency Shutdown Valve" and you have a twenty second
>delay I would be worried.
>
>Our Australian Gas Code as well as "Good Engineering
>Practice" would expect a closure of between 2 to 3 seconds
>maximum.